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A subsidiary of Twin Metals will be allowed to drill six exploratory boreholes near and around Birch Lake in St. Louis County — all within the watershed of the Boundary Waters Canoe Area Wilderness.

The Minnesota Department of Natural Resources approved the drilling plan from Franconia Minerals LLC on Monday. The approval requires the company to avoid clearing plants and disturbing ground outside of an access road, and to take measures to dampen noise from the work. Drilling will be allowed through March 2025.

The letter also notes that Twin Metals has the right to drill two additional boreholes that would not use state minerals, and thus don't require DNR approval.

The drilling plan, which was submitted to the DNR in September, is a sign Twin Metals has not given up on developing a Minnesota hardrock mine, even though another project it proposed a few miles to the northeast has been largely blocked by a federal drilling ban.

Twin Metals Minnesota is a wholly owned subsidiary of the Chilean mining giant Antofagasta PLC.

Kathy Graul, a spokeswoman for Twin Metals, wrote in an email that "we look forward to beginning exploration activity in a safe and environmentally responsible manner over the coming months, with a goal of collecting key data about our critical mineral resources."

Erik Evans, a spokesman for the DNR, said in an email that the agency has never denied an exploratory drilling plan for a company that already holds mineral leases. The agency said state law requires it to approve leaseholders' exploration requests. Northeastern Minnesotans for Wilderness (NMW), an environmental advocacy group, had asked the agency to deny Franconia's request.

The group also sued the DNR in 2020, saying that the state's rules for siting hardrock mines were insufficient to protect the Boundary Waters. The DNR re-examined its policies as a result of that suit and determined earlier this year that its mining rules did not protect the wilderness from light and noise pollution. The agency indicated it would change its rules to stop those potential disturbances.

By allowing Twin Metals' latest plan when there are still legal questions about siting a mine in this area, "this is shortcutting the process," said Ingrid Lyons, executive director of Northeastern Minnesotans for Wilderness.

The group and Twin Metals have both asked for an evidentiary hearing that challenges the DNR's potential rule changes. NMW says it did not go far enough to protect water quality, while Twin Metals argues it went too far with moves to cut light and noise pollution. The hearing has not yet been scheduled.

Correction: Previous versions of this story did not fully state DNR's position on mineral exploration review.